Collaborative Research: Phylogeny of the Triassic-Recent Nautilaceae (Cephalopoda)

9614327沃德鹦鹉螺目头足类包括20多个属和数百个命名物种，跨度近2.3亿年(三叠纪-最近)。它们的历史和系统发育一直被认为是很清楚的，它们的系统学在近50年来一直保持相对不变，在此期间有三个原则没有受到挑战：1)鹦鹉螺在进化上是保守的，自三叠纪末以来形态变化很小；2)大多数属只能通过一两个特征来区分；3)最后进化的成员是现存的鹦鹉螺，进化于更新世或上新世。然而，在过去的十年里，新的信息表明，对该类群的系统发育解释和分类进行彻底的重新评估是必要的。现在看来，后侏罗纪鹦鹉螺属的物种已经大大超过了狭缝；新的化石发现表明，鹦鹉螺属至少可以追溯到白垩纪中期；最近的调查显示，几个新的特征将有助于对该群的分支学评估；对鹦鹉螺科的初步系统发育分析与过去的解释截然不同。我们建议开发一套形态特征，使我们能够对该类群进行分支分析，以发展对进化关系的理解，并根据我们对变异和物种以及现存分类群中的属概念的理解来评估命名化石分类群的有效性。我们将使用共享派生字符的存在来开发基于进化关系而不是形态相似性的群体分类系统。此外，我们建议使用主成分分析(PCA)来：a)量化和跟踪形态随时间的变化和多样性；b)确定特定的贝壳形态是否是首选的，以及在极长的时间跨度(200my)上理论形态与占据形态空间之间的关系；以及c)评估这些形态如何响应生物危机，重点关注三叠纪和白垩纪末期的灭绝事件。我们的研究结果将直接关系到了解这一特殊谱系的进化史，它是范围最长的软体动物支系之一，从最近到三叠纪(约2.3亿年)。这些结果将对解释近2亿年尺度上形态多样性和丰富度的宏观进化变化，以及对生物危机的形态响应产生影响。

9614327 Ward Nautilacean cephalopods include more than a score of genera and hundreds of named species spanning almost 230 million years (Triassic-Recent). Their history and phylogeny have been thought to be well understood, and their systematics have remained relatively unchanged for ~50 years, during which three tenets have remained unchallenged: 1) nautilaceans were evolutionarily conservative, showing little morphological change since the end of the Triassic; 2) most genera can be differentiated by only one or two characters; and 3) the last-evolved member is extant Nautilus, having evolved in the Pleistocene or Pliocene. In the last decade, however, new information suggests that a radical re-evaluation of both the phylogenetic interpretation and the classification of the group are in order. It now appears that post-Jurassic nautilacean species have been vastly over-slit; new fossil finds show that the genus Nautilus dates back at least to the middle Cretaceous; recent investigations demonstrate several new characters that will aid in the cladistic evaluation of the group; and preliminary phylogenetic analysis of the Nautilaceae stands in marked contrast to past interpretations. We propose to develop a suite of morphologic characters that will permit us to undertake cladistic analysis of the group, in order to develop understanding of evolutionary relationships, and to assess the validity of named fossil taxa in the light of our understanding of variation and species-and generic concepts in extant taxa. We will use the presence of shared derived characters to develop a classification system of the group, based on evolutionary relationships, rather than morphological similarity. In addition, we propose to use principal components analysis (PCA) in order to: a) quantify and to track morphologic variation and diversity through time; b) determine whether (which) particular shell morphotypes were preferred and the relationship between theoretical and occupied morphospace over an extremely long time span (200 my); and c) assess how these morphologies responded to biotic crisis, focusing on the terminal Triassic- and Cretaceous extinction events. The results of our investigation will bear directly on understanding the evolutionary history of this particular lineage, one of the longest ranging of molluscan clades, extending from the Recent to the Triassic (~230 million years). The results will have bearing on the interpretation of macroevolutionary change in morphologic diversity and richness, and to morphologic responses to biotic crisis, on a scale of nearly 200 million years.